This invention relates to a snubber for a dipper door. More specifically, it relates to a snubber which retards movement of the door when it is at certain angular positions with respect to an opening defined in the dipper.
Large excavator dippers have heavy doors which move to open or close an opening defined in the dipper. In a typical 15 cubic yard dipper the door weighs approximately 12,000 pounds. In operation, digging is begun with the door in a closed position. When the bucket is full of mined material, the dipper is elevated and rotated approximately 90.degree. such that the door is approximately parallel with respect to the ground and moved to a discharge location, such as over a dump truck bed. The door then is released which permits it to pivot from the horizontal position to a substantially vertical position with respect to the ground to permit the mined material to be discharged through the opening. Subsequently, the bucket is rotated toward the door to cause the door to close the opening.
If movement of the heavy door is not retarded before it contacts the dipper on closing, it may slam into the dipper with such force that damage to the door, the door hinge, or the dipper will result. Likewise, if movement of the door is not retarded as it approaches the limit of its travel away from the opening, the door may slam into the handle causing damage to it or to the door. Consequently, it is desirable to have a device which will snub movement of the door when it approaches the dipper to close the opening or when it approaches the handle.
In the past, a number of snubbers have been developed which connect between the door and the dipper to retard movement of the door. The majority of these snubbers have incorporated springs, friction elements or hydraulic elements. Each of these has certain disadvantages in commercial use. For example, coil springs generally do not create sufficient force to retard door movement under all conditions and can be fouled by rocks which become wedged between coils. Hydraulic devices are subject to leakage and are easily damaged when struck by mined material. Friction devices require constant adjustment and have a relatively short useful life. One form of snubber which has proven effective and has eliminated many of the disadvantages of previous snubbers is one having a unitary elastic body which is described in detail in U.S. Pat. No. 4,443,957 which is assigned to the assignee of the instant invention. This device has an elastomeric working section which interconnects a pair of end lugs having mounting holes. The mounting holes are offset from the longitudinal center line of the working section and are attached by pivot pins to the dipper and to the door. In a position intermediate one extreme position in which the door closes the opening defined in the dipper and the other extreme position in which the door is approximately perpendicular with respect to the opening, the snubber is in an unstressed condition. As the door moves toward the opening the elastomeric working section is placed in tension to retard this movement. When the door is moved from the intermediate position toward the other extreme position the working section is placed in bending to retard this movement. Although the unitary elastic body snubber has eliminated many of the disadvantages found in other types of snubbers it has been found that in heavy usage it has a shorter than desired useful life.
Research has disclosed that one reason for the shorter than desired useful life of the elastic snubber is that the working section is stressed any time the door is moved from the intermediate position. It was found that the useful life of the snubber could be greatly increased if it were not stressed at all angular positions of the door with respect to the opening but instead is placed in tension to retard movement of the door toward the dipper only when the door was within a first specified angular position with respect to the opening, is placed in bending to retard movement of the dipper arm away from the dipper only when the angle of the door with respect to the opening exceeds a second specified angular position, and is unstressed when the door is between the two positions.